1. Field of the Invention
The invention relates to an optical connector for connecting optical fibers.
2. Description of the Related Art
In an optical connector that connects optical fibers, (1) reflected return rays at a connecting node must be reduced (implementation of low reflection); and (2) rays not being propagated to the light-receiving side due to their returning backward or being scattered by reflection at a connecting node must be reduced (reduction in reflection loss).
To meet these requirements, physical contact (PC) coupling (direct contact coupling between optical fibers) is under study for single fiber connectors. For example, a polishing wheel dedicated to optical connectors such as disclosed in Unexamined Japanese Patent Publication No. Sho. 61-137107 has been developed.
On the other hand, for multi-fiber connectors, it is difficult to achieve physical contact coupling for all the fibers. Conventionally, in order to reduce reflection, the end surfaces has been polished obliquely to connect the polished surfaces. However, since this method is not successful to get rid of reflection loss, the optical connectors are coupled by interposing an index matching agent having substantially the same refractive index as that of the optical fiber core between the end surfaces of the optical fibers.
However, the connection made by interposing the index matching agent between the end surfaces of the optical fibers must involve the step of applying the index matching agent. Accordingly, this structure has a disadvantage in terms of operability and handling and, in addition, easily admits contaminations between the end surfaces of the optical fibers, which is a problem.
In view of such circumstances, a coupling method without using the index matching agent has been under study for multi-fiber connectors. Unexamined Japanese Patent Publication No. Hei. 4-34403 discloses a method of connecting optical connectors in which a resin film having a refractive index close to that of the fiber is arranged at an end surface of the optical connector to connect the optical connectors through the resin film.
However, according to the above-mentioned method of providing a resin film having a refractive index close to that of the core on the end surface of the optical connector, a thin resin film is present on the end surface of the optical connector. Accordingly, such an optical fiber not only impairs reliability for the function of coupling the optical connectors over a long period of time, but also leads to a disadvantage in corrosion resistance as well as coupling strength. In addition, if the thickness of the resin film is increased to increase the strength of the resin film, connection loss increases.
A technology for achieving physical contact coupling of all the fibers of multi-fiber connectors in a manner similar to the case of single core connectors has been developed. However, it is difficult to project only the optical fibers stably from the end surface of the optical connector by controlling condition for polishing the entire surface of the ferrule of the multi-fiber connector. Particularly, since a filler, one of materials forming the ferrule, is contained in the ferrule for enhancing the stableness of the size of the ferrule, the filler is easy to project from the polishing surface. Accordingly, it is difficult to project only the optical fiber from the polished end surface of the optical connector. In addition, even if the end surfaces of the optical fibers is projected, the end surfaces of the respective optical fibers are not oriented in the same direction, but in fact, there is a variation of about 0.2.degree. in the inclination of the respective end surfaces. This brings about a problem that coupling between the respective optical fibers becomes unstable.